The audio and/or video apparatus is popular in people's lives. There are energy converters for converting sound energy to electric energy mutually in audio and/or video, such as loudspeakers, earphones and sonic transducers (microphones). The energy conversion between electricity and sound is performed by applying a magnetic field on a current-carrying conductor in a converter which comprises the driving system, vibrating system and supporting system. The electromagnetic energy converters with drive coils and inductance are employed in the driving system. The inductive impedance changes with the variation of frequency, i.e., when the frequency rises, the inductive impedance increases so that the obtained energy of the electromagnetic energy converter changes, which will lead to the change of driving force. At the same time, because of the existence of inductance, the phase shifts will occur due to the voltage and the current through the loudspeaker, which will lead to defective feedback to the power amplifier used for driving the loudspeaker. Moreover, due to the effects of conversion between electric energy and magnetic energy and the magnetic hysteresis, the energy supplied to the drive coil of the loudspeaker will excite the magnetic circuit of the loudspeaker to generate magnetic energy that is stored in the magnetic circuit system of loudspeaker. When the phase of voltage changes in combination with the effect of magnetic energy converting to electric energy, the energy stored in the magnetic circuit of loudspeaker will act on the drive coil via the differential resistance of the power amplifier, which will lead to frequency response and distortion of the loudspeaker, earphone and sonic transducer.
As far as the inventor of this invention knows, a short-circuit ring 8 was installed in the sensitive position of drive coil 2 to reduce the harmful excitation of the drive coil to the magnetic circuit system and the inductance quantity of electromagnetic drives in some products in the prior art (as shown in FIG. 11), and the short-circuit ring which is generally a conductor such as copper is made into a closed ring and mounted around the periphery of magnetic pole 1. But because only part of the energy produced by drive coil can just be passively consumed by the short-circuit ring, and the short-circuit ring is not connected electrically with the drive coil, the short-circuit ring may not apply positive and equivalent feedback excitation to the magnetic circuit system to counteract the harmful excitation of the drive coil on the magnetic circuit system. The effectiveness is limited, so they are different from this invention.